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Construction of precast walls are very rigid since the element are inherently stiff to begin with. Therefore, it is important to detail the connections in such a way to ensure robustness in the event of a natural disaster such as earthquake and absorb its energy to avoid complete collapse.

There are a number of challenges when connecting precast walls, namely:

1. Connections are wet, so require temporary bracing.
2. Installation time can be lengthy, so crane time is not optimised.
3. Connecting of both vertical and horizontal rebar connections is practically impossible due to the stiffness of the rebars.

At Leviat, we have a solution for all of these challenges, but here we would like to address the third one as it is arguably the most important fundamental.

So What is MOMENT Loop Box?

MOMENT Loop Box are used for connecting precast wall to wall or to a column. After casting to the formwork, the precaster will just need to remove the tape and release the loop into the operating position. A vertical rebar (sometimes called a trimmer or cottering bar) is installed into the joint through the wire loops. Lastly, cementitious grout is poured or pumped into the joint.

There are 3 types of MOMENT Loop Box – Multi, Double and Single Loop Box.

Loop boxes are installed to the formwork according to the spacing specified by the designer, before the panel is cast.

A vertical rebar is installed into a joint through the wire loops of both precast panels before grouting.

Key Advantages

Fully compliant with EN1992-1-1 (Eurocode 2), MOMENT Loop Box has been tested in accredited test labs to simulate performance in various application, transmitting forces from three directions (perpendicular, parallel and transverse load).

Below are the key advantages of loop box when compared with the traditional method of connecting precast walls:

1. Flexible installation method for seamless connection between precast wall
2. Reduces the total installation time by 50% with less labour
3. Eliminates the clashes between U-bars from the traditional method
4. Customizable length of steel box and wire loops
5. Easy installation of loop box to the formwork with the option of magnet

Multi loop box acts as a shear key and simplifies the design of the formwork.

Making precast wall connection easier and faster

Key Features

Consists of high-strength, galvanized steel casing and wire loops, loop boxes connect precast walls in an efficient and time saving method. Below are the key features of loop box:

Galvanized Steel Box
A robust sheet-steel box and wire loops contain the plastic latch and wire loops

Plastic Latch
Specially designed plastic latch to secure the wire loops in position for good anchorage embedment for in concrete
 

Flexible wire loops
Galvanized wire loops transmit force into the concrete and connect 2 walls to each other. Loops can be bent out and straightened with a hammer claw, screwdriver or a nail.

MOMENT Loop Box Makes Wall Connection Easier.
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The precast joint connections on construction sites has always been a difficult challenge due to manufacturing tolerances and the need to transfer loads through the structure; even more so when you factor in a required resilience to a seismic events. Precast components are inherently stiff, so it is essential that the precast concrete connections are robust enough to allow the structure to absorb the energy of the earthquake, whilst providing enough robustness to avoid collapse.

There are a number of ways of doing this such as via:
• Grouted Coupler for precasts walls and columns to foundations connection
• Wire Loop Box for precast walls connection
• Precast Coupler for precast elements connection
• Dowel Systems for precast beam to column connection

Apply the latest technology of precast connections from Leviat, available in Malaysia, Singapore, India & the Philippines. Discover more now!

Grout coupler are traditionally used in the bottom of a column or wall as a means to connect on to starter bars protruding from the foundation. Although they might often be designed as a pin connection, the reality is that this will transfer moment from the foundation in to the wall or column and should therefore always be made of a ductile material that does not compromise the ductility of the steel reinforcement that it is coupling together. To that end, the coupler should always be of a “bar break” type where there is a considerable factor of safety between the bar failure and the coupler failure capacities.

Loop boxes are prefabricated components with a constant rebate geometry and 1 or 2 high strength (c. 1600-1800MPa) wire loops. Loops from adjacent elements then overlap during installation of the panels and are secured using a reinforcing bar and a high early strength grout to complete the connection.

They are usually used to connect 2 adjacent precast panels together, where the interlocking rebar and wire loops provides robustness in the event of an Earthquake to ensure that grout degradation would not result in complete collapse.

Connection Loop is a single-wire loop used to connect 2 precast boxes for the prefabricated prefinished volumetric construction (PPVC).

In order to connect 2 precast elements, both precast elements has to be cast with the MOMENT Connection Loop at the wall. A rebar will then be inserted through the intersection of 2 loops. After placing the rebar, the gap between the precast elements will need to be grouted using a 40Mpa or 70MPa non shrink grout depending on the application. Material strength of the MOMENT Connection Loop is 1770N/mm  and complies to EN12385-4:2002+A1.

The HEK Precast coupler is an innovative and versatile solution for fast and easy connection of precast concrete elements.

Cast-in DEMU Fixing anchors i.e. T-FIXX^®, bolt or bar anchors transfer the tension and shear force into the precast element.

The main advantage of the system is the fast and efficient positioning of precast elements. The connection can be subjected to load immediately after installation. This results in a substantial improvement in construction time.

Shear dowel systems are always a challenge as they generally require very tight tolerances to ensure effective load transfer, so systems without grout and oversized holes are almost impossible. Traditionally, precast slabs such as stair landings used to be supported by a steel angle bolted to the wall. Installation was slow, required high degrees of accuracy, tied up the crane with costly hook- time and could only be used on straight walls.

But by keeping the grouting to a minimum, one such technology – Invisible Connections – has revolutionized the use of precast all throughout Northern Europe; it is a patented system, with its origins in Norway, to connect precast concrete without use of corbels or steel angles, and is used extensively throughout Europe due to the independently tested and certified European Technical Approval (ETA [4]) that provides engineers with peace of mind about the capacities.

The product range of Invisible Connections consists mainly of TSS Telescopic Stair Connectors & BSF Telescopic Beam Connectors.

         

Another topic relating to Invisible Connections will be covered as a future topic in our Academy site.

There are many good technologies available, but a dependence on local testing and local reference projects will hinder and slow down their introduction. An increased readiness to accept the certification schemes for prequalification that exist overseas such as ETA[4] and ICC certification where appropriate, will mean that the technologies can help keep pace with the requirements of the precast industry.

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The connection between precast concrete is a safety critical component in today’s structural precast construction. The success of this construction method goes beyond the structural performance of precast beams and columns; it also includes the performance of the precast connection. For the connection, the performance is not only limited to the structural robustness, but also embodies simplicity and productivity during the erection process. The connection types employed will not only affect the construction cost and speed but also have an impact on the sections that can be used via the ability for forces and moments to be redistributed throughout the finished structure.

Moment Grout Coupler, consists of a one piece design, is a rebar coupler designed for precast connections. Compliant with ISO 15835, each grout coupler combines the benefits of the Moment JT threaded system and will achieve barbreak when used together with Moment’s proprietary 100MPa grout.*

Specifically for precast connections, Grout Coupler can be used for connecting precast walls, columns, beams either horizontally or vertically. The most popular connections used with Grout Coupler are:

1. Precast concrete column to foundation connection
2. Precast column to column connection
3. Precast beam to column connection

For this type of connection, the high tensile steel starter bars are left protruding from the foundation. After that, a precast column with vertical sleeves at the end is placed over the starter bars. The sleeves are the filled in with grout to provide a connection. This connection has the ability to provide moment resistance at the connection between column end to footing. Additional technologies such as precast shoes can then be used to eliminate the need for propping.

Similar to the above application, this enables the launching of one column section on top of another one whilst providing full moment continuity across the joint. This is specifically important on projects with large column sections as the height of the element is often limited to less than 1 storey because of crane capacity limits.

You can use grout couplers to overcome one of the biggest challenges in precast concrete construction; a moment resisting frame. In this application, you provide clearance holes through the precast column and use a grouted coupler to provide full continuity through the precast column.

To broaden the field of application, two product types are available: Full Grout Coupler and Half Grout Coupler. The rebars used with a Full Grout Coupler require no bar end preparation, such as threading, and are simply inserted to meet at the nominal centre point of the coupler.

For more information on Moment Grout Coupler, please contact our offices where we can showcase you the actual Grout Coupler as well as our latest innovative precast accessories.

*Lower grout grades might be possible, but it depends on the rib profile of the individual rebar supplier.

Connect Precast Elements The Easy Way.
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